How does the illumination mechanism of a planetary nebula differ fundamentally from a reflection nebula?
Answer
Planetary nebulae rely on internal UV ionization from a dying star, unlike reflection nebulae which scatter existing starlight off dust.
Planetary nebulae are powered internally by the UV output of the central white dwarf exciting its own expelled gas (fluorescence/emission), whereas reflection nebulae simply scatter ambient starlight off dust grains without requiring intense ionization.
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